RF power transistor circuits

ABSTRACT

A radio frequency (RF) power transistor circuit includes a power transistor and a decoupling circuit. The power transistor has a control electrode coupled to an input terminal for receiving an RF input signal, a first current electrode for providing an RF output signal at an output terminal, and a second current electrode coupled to a voltage reference. The decoupling circuit includes a first inductive element, a first resistor, and a first capacitor coupled together in series between the first current electrode of the power transistor and the voltage reference. The decoupling circuit is for dampening a resonance at a frequency lower than an RF frequency.

RELATED APPLICATION

This application is a continuation of co-pending, U.S. patentapplication Ser. No. 14/185,382, filed on Feb. 20, 2014, which is acontinuation of U.S. Pat. No. 8,659,359, issued on Feb. 25, 2014, whichwas a National Stage Entry under 37 C.F.R. 371 of PCT/IB2010/001283,filed on Apr. 22, 2010.

BACKGROUND

Field

This disclosure relates generally to semiconductors, and morespecifically, to the radio frequency power devices.

Related Art

In the field of wireless communication, integrated circuits commonlyimplement radio frequency power amplifiers (RFPAs) which supply anamplified amount of output power. The operating frequencies for wirelesscommunication have increased as the demand for wireless communicationhas increased. RF power amplifiers must have sufficient gain andbandwidth for operation well into the gigahertz range. Conventional RFpower amplifiers have an upper limit to the bandwidth of the inputsignal that can be amplified before incurring excessive distortion andruggedness issues. As signal bandwidth is increased, conventional RFpower amplifiers exhibit increased distortion in the sidebands.Additionally, high voltage excursions are present on the drain electrodeof the power transistor used for amplification. The bandwidth limitationimposed on RF power amplifiers is caused by several sources. One sourceof the bandwidth limitation is due to impedance resonances loading thegate and drain of the power transistor. The interaction betweencomponents which are internal to the pre-matched RF power transistor andexternal circuit board components creates resonances at frequencies thatare of the order of the modulation bandwidth of the RF signal.

Another aspect of RF power amplifier operation is the use of DigitalPre-Distortion (DPD). Digital Pre-Distortion is a system which is usedin conjunction with RF power amplifiers to reduce the level ofdistortion and thereby comply with linearity specifications.Conventional DPD systems perform well for RF power amplifiers up tosignal bandwidths where the baseband impedance is low and the phase isclose to linear. However, any kind of resonance or rapid phasetransition presents a hard limit for Digital Pre-Distortion correction.

Another behavior of RF power amplifiers is the presence of a lowfrequency gain peak which is attributable to the pre-matched RF powertransistor. This gain peak is out-of-band but it is important that thepeak be as low as possible. The low frequency gain peak can causestability issues, as well as linearization problems when using a DPDsystem. Conventional RF power amplifiers generally do not have all ofthe characteristics of very high signal bandwidth, low RF powertransistor drain voltage swing, good digital pre-distortion correctionand low out of band gain peaks.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and is notlimited by the accompanying figures, in which like references indicatesimilar elements. Elements in the figures are illustrated for simplicityand clarity and have not necessarily been drawn to scale.

FIG. 1 illustrates in graphical form a plot of power and frequency of apower amplifier response of a power amplifier that uses a prior artimplementation of a decoupling network;

FIG. 2 illustrates in graphical form a plot of power and frequency of apower amplifier response of a power amplifier that implements adecoupling network embodying principles of the present invention;

FIG. 3 illustrates in schematic diagram form a power transistor circuitembodying principles of the present invention;

FIG. 4 illustrates in schematic diagram form another power transistorcircuit embodying principles of the present invention;

FIG. 5 illustrates in schematic diagram form yet another powertransistor circuit embodying principles of the present invention;

FIG. 6 illustrates in schematic diagram form yet another powertransistor circuit embodying principles of the present invention;

FIG. 7 illustrates in schematic diagram form a portion of another powertransistor circuit embodying principles of the present invention;

FIG. 8 illustrates in schematic diagram form another power transistorcircuit embodying principles of the present invention;

FIG. 9 illustrates in schematic diagram form another power transistorcircuit embodying principles of the present invention;

FIG. 10 illustrates in schematic diagram form another decoupling circuitfor use in any of the illustrated power transistor circuits;

FIG. 11 illustrates in schematic diagram form another power transistorcircuit embodying principles of the present invention;

FIG. 12 illustrates in graphical form a two-tone frequency response of aknown power amplifier circuit with a decoupling network that providesinstantaneous bandwidth capability of no more than 75 MHz;

FIG. 13 illustrates in graphical form a two-tone frequency response of aknown power amplifier circuit with a wide instantaneous bandwidthdecoupling network having an unwanted low frequency resonance; and

FIG. 14 illustrates in graphical form a two-tone frequency response ofany of the power transistor circuits embodying principles of the presentinvention.

DETAILED DESCRIPTION

There is disclosed herein a power transistor circuit for use in a poweramplifier that uses a frequency decoupling network capable ofcommunicating high instantaneous bandwidth signals. A decoupling circuithaving an inductive element, a resistive element and a capacitor iscoupled together in series between a control electrode of a powertransistor and a power supply terminal. The decoupling circuit dampens aresonance at a frequency lower than an RF frequency. The disclosedstructure provides an RF power amplifier having low baseband impedanceacross an entire signal bandwidth and permits significantly increasedvideo bandwidth. Low frequency resonance is corrected by the decouplingcircuit and low frequency phase transition is eliminated to ensure gooddigital pre-distortion performance. The resistive element of thedecoupling circuit permits pre-distortion linearization of signals withvery closely spaced carriers and thus provides improved digitalpre-distortion linearization.

Illustrated in FIG. 1 is a plot of power and frequency of a poweramplifier response of a power amplifier implementing a decouplingnetwork which is intended to improve instantaneous bandwidth. Twosuperimposed frequency responses are illustrated in FIG. 1 having twoclosely spaced carriers or channels. A frequency response 10 isillustrated having an in-band range in the middle of the illustratedfrequency response. Without the use of digital pre-distortion, thefrequency response 10 exhibits a significant non-linear power responseat both low-band and high-band. This out-of-band power representsdistortion in the sideband frequencies. Frequency response 12illustrates when digital pre-distortion is used in the power amplifier.With digital pre-distortion the amount of power reduced in the sidebandfrequencies is limited, due to low frequency resonances present in theconventional decoupling network. As the spacing of the two carriersignals are moved farther apart, the low frequency resonances in thedecoupling network become inconsequential since the envelope frequenciesthat cause the distortion products are now higher than the low frequencyresonance. This prior art decoupling network improves the upperfrequency limit of instantaneous bandwidth capability, butclosely-spaced signals have very poor distortion correction.

Illustrated in FIG. 2 is a plot of power and frequency of a poweramplifier response of a power amplifier that implements a decouplingnetwork in accordance with principles of the present invention. Theillustrated decoupling network that is connected to the gate and/ordrain of a power transistor provides low baseband impedance across anentire signal bandwidth. The frequency response 14 shows that withoutdigital pre-distortion, there is significant power (i.e. distortion) inthe low-band and high-band frequency ranges. The frequency response 16,which is superimposed with frequency response 14, shows a largereduction in the power of the side bands, even at frequencies just aboveor below the carrier. The illustrated decoupling network improves boththe high instantaneous bandwidth capability, as well as distortioncorrection of closely-spaced signals. Discussed herein will be circuitsand methods for keeping the higher instantaneous bandwidth capability,while also allowing distortion correction of closely-spaced signals. Byway of example only, in one form the represented instantaneous bandwidthfrequencies are a range of frequencies from D.C. to around the 500 MHzrange. The in-band or passband range of frequencies is from around 1.6GHz to 3.7 GHz.

Illustrated in FIG. 3 is a circuit 20 that is an output portion of an RF(radio frequency) power amplifier. An RF input signal is coupled to anRF input terminal 22 and an amplified RF output signal is provided at anRF output terminal 24. The circuit 20 generally has a power FET 26(i.e., RF power Field Effect Transistor) and a power FET 28 with eachhaving a gate, a drain and a source. In the illustrated form, the powerFETs 26 and 28 each are N-channel devices. A gate-side RF matchingnetwork 30 is connected between the RF input terminal 22 and the gate ofthe power FET 26. A gate-side RF matching network 32 is connectedbetween the RF input terminal 22 and the gate of the power FET 28. Agate-side decoupling circuit 34 is connected between a ground V_(SS)terminal and each of the gates of power FET 26 and power FET 28. Thedrain of each of power FET 26 and power FET 28 is connected to the RFoutput terminal 24. A power supply voltage labeled V_(DD) is connectedto the drains of power FET 26 and power FET 28 at the RF output terminal24. A drain-side decoupling circuit 64 is connected between the drain ofeach of power FET 26 and power FET 28. Each of power FET 26 and powerFET 28 has a source connected to the ground V_(SS) terminal. A conductorhaving an inductive element in the form of an inductance 40 that isinherent in the conductive material of the conductor is connectedbetween the RF input terminal 22 and a node 36. It should be understoodthat the conductor may be implemented in various forms. For example, aconductive or metal wire may be used as the conductor. A conductivelayer or conductive strip commonly used in semiconductor manufacturingmay be implemented from any of various conductive materials, such asmetals including copper, tungsten and various metal alloys. A firstelectrode of an RF matching capacitor 38 is connected to node 36. Asecond electrode of the capacitor 38 is connected to the ground V_(SS)terminal. The node 36 is connected to the gate of the power FET 26 by aconductor having an inductance 42 that is inherent in the conductivematerial of the conductor.

Within the gate-side decoupling circuit 34, a node 52 is connected tothe gate of the power FET 26 by a conductor having an inductance 50 thatis inherent in the conductive material of the conductor. Node 52 is alsoconnected to the gate of the power FET 28 by a conductor having aninductance 62 that is inherent in the conductive material of theconductor. A first terminal of a resistor 54 is connected to the node 52and a second terminal of the resistor 54 is connected to a firstelectrode of a low frequency decoupling capacitor 58 via a conductorhaving an inductance 56 that is inherent in the conductive material ofthe conductor. The first electrode of the decoupling capacitor 58represents a decoupled node 60. A second electrode of the decouplingcapacitor 58 is connected to the ground V_(SS).

Within the gate-side RF matching network 32, the RF input terminal 22 isconnected to a node 44 via a conductor having an inductance 46 that isinherent in the conductive material of the conductor. A first electrodeof an RF matching capacitor 45 is connected to node 44, and a secondelectrode of the RF matching capacitor 45 is connected to the groundV_(SS). The node 44 is connected via a conductor having an inductance 48that is inherent in the conductive material of the conductor to the gateof the power FET 28 and to the conductor having inductance 62.

Within the drain side of power FET 26, a conductor having an inductance66 that is inherent in the conductive material of the conductor has afirst end connected to the drain of power FET 26 and a second endconnected to a node 71. A conductor having an inductance 63 that isinherent in the conductive material of the conductor has a first endconnected to the drain of power FET 26 and a second end connected to theRF output terminal 24. A first electrode of a D.C. blocking capacitor 67is connected to node 71. A second electrode of the D.C. blockingcapacitor 67 is connected to the ground V_(SS). Within the drain-sidedecoupling circuit 64, a conductor having an inductance 75 that isinherent in the conductive material of the conductor has a first endconnected to the node 71 and a second end connected to a first terminalof a resistor 77. A second terminal of the resistor 77 is connected to afirst end of a conductor having an inductance 79 that is inherent in theconductive material of the conductor. A second end of the conductorhaving the inductance 79 is connected to a first electrode of adecoupling capacitor 81. A second electrode of the decoupling capacitor81 is connected to the ground V_(SS). A conductor having an inductance69 that is inherent in the conductive material of the conductor has afirst end connected to the drain of power FET 28 and a second endconnected to a node 73. A first electrode of an RF matching capacitor 70is connected to node 73. A second electrode of the RF matching capacitor70 is connected to the ground V_(SS). Within the drain-side decouplingcircuit 64, a conductor having an inductance 83 that is inherent in theconductive material of the conductor has a first end connected to thenode 73 and a second end connected to the first terminal of the resistor77.

In operation, circuit 20 implements two power FETs that have theirrespective gates coupled to the RF input terminal 22 and theirrespective drains coupled to the RF output terminal 24. It should beunderstood that in another form only one power FET, such as power FET 26may be implemented. In that form, inductances 46, 48, 62, 65, 69 and 83,capacitors 45 and 70 and power FET 28 are not present. In theillustrated form of FIG. 3 circuit 20 receives an RF input signal andselectively amplifies or increases the power of the RF signal to providean amplified RF output signal at output terminal 24. The RF outputsignal is superimposed onto the terminal for the supply voltage V_(DD).

The RF matching networks 30 and 32 function to raise the impedance atthe RF input terminal 22. Because the impedance of the gate of each ofpower FET 26 and power FET 28 is low, the RF matching networks 30 and 32are needed to more closely match the impedance of the circuitry (notshown) that is coupled to the RF input terminal 22 for providing an RFinput signal. A closely matched impedance avoids a power loss or gainloss of the RF signal on the gate side of each of power FET 26 and powerFET 28. The values of the inductances 40 and 42 and capacitor 38 as wellas the value of the inductances 46 and 48 and capacitor 45 are chosen toraise the input impedance to a predetermined input impedance. The knowninput impedance allows an outside user to present a matching impedanceto the circuit 20. On the drain side of power FET 26, capacitor 67 alsofunctions as part of an RF matching circuit to provide, along withinductances 66 and 63, an impedance to the RF output terminal 24 toavoid a power loss or gain loss. Similarly, on the drain side of powerFET 28, capacitor 70 also functions as part of an RF matching circuit toprovide, along with inductances 65 and 69, an impedance to the RF outputterminal 24 to avoid a power loss or gain loss. A user can thereforeclosely match the impedance of circuitry that is coupled to the RFoutput terminal 24 to prevent a performance loss. The gate sidedecoupling network 34 presents a high impedance to the passband range offrequencies and above. The gate side decoupling network 34 is functionalin the low band range of frequencies. In particular, the gate sidedecoupling network 34 provides a low impedance termination to ground forthe distortion products that develop due to envelope frequencies. Thegate side decoupling network 34, in the absence of resistor 54, exhibitsa low frequency resonance which is undesired. In particular, theinductor/capacitor circuit by itself creates an unwanted resonance inthe 1 to 20 MHz range which interferes with pre-distortion linearizationand creates a high impedance at very low baseband frequencies. However,resistor 54 is inserted between the gate of the power FETs 26 and 28 andcapacitor 58 to dampen or attenuate the low frequency resonance createdby the gate side decoupling network 34. The low frequency resonancewhich is dampened by the resistor is at a frequency that is lower thanan RF frequency. By dampening the low frequency resonance, digitalpre-distortion effectively reduces distortion in the side bands, evenwith very closely-spaced carriers.

Similarly, the decoupling circuit 64 presents a high impedance to thepassband range of frequencies and above on the drain side of each ofpower FETs 26 and 28. The decoupling circuit 64 is functional in the lowband range of frequencies. In particular, the decoupling circuit 64provides a low impedance termination to ground for the distortionproducts that develop due to envelope frequencies. The decouplingcircuit 64, in the absence of resistor 77, exhibits a low frequencyresonance which is undesired. However, resistor 77 is inserted betweenthe drain of the power FETs 26 and 28 and capacitor 81 to dampen orattenuate the low frequency resonance created by the decoupling circuit64. It should be noted that at node 71, the signal path throughinductance 75, resistor 77, inductance 79 and capacitor 81 is a highimpedance path which blocks the RF signal from being attenuated byresistor 77. The same is true at node 73 with respect to inductances 83and 79, resistor 77 and capacitor 81. Thus, at the drain of power FET 26the RF signal is coupled to the RF output terminal 24 except for a smallportion of RF which is lost via matching capacitors 67 and 70 which arelow impedance. Thus the drain side of each of power FET 26 and power FET28 has low RF loss. Within the decoupling circuits 34 and 64 theinductive elements as represented by the inductances provide for directcontrol of where low frequency resonance occurs. Therefore it isimportant to have the values of the inductive components be as small aspossible. The capacitors within the decoupling circuits 34 and 64provide for good low-frequency short circuiting for decoupling. Hence itis important to get the capacitive value of capacitors 58 and 81 as highas possible. However, with current multiple layer capacitor technology,it is difficult to get a very high valued capacitor with a desired formfactor and breakdown voltage. Hence practical limitations force thesecapacitors to have a value that is limited to the hundreds of nanoFaradsrange. As a result, the LC components of the decoupling circuits 34 and64 create the unwanted resonance in the 1-20 MHz range which interfereswith pre-distortion linearization. Thus the use of resistors 54 and 77to dampen this resonance provides a noticeable reduction in basebandimpedance across the signal bandwidth and allows the use ofclosely-spaced signals with digital pre-distortion.

In another form of circuit 20, two RF outputs rather than a single RFoutput at terminal 24 may be implemented. In this alternate form, thesecond terminal of inductance 65 is not connected to terminal 24 butrather is left unconnected as a second RF output. The power supplyvoltage V_(DD) is also connected to this second RF output. The modifiedcircuit 20 provides a dual path device and is a balanced configuration.The two outputs can be used either in a push-pull configuration or in aDoherty amplifier configuration. The power combining of the two RFsignal paths is implemented external to circuit 20.

Illustrated in FIG. 4 is a circuit 84 that is a portion of another poweramplifier in accordance with another form. An RF input signal is coupledto an RF input terminal 85 and an amplified RF output signal is providedat an RF output terminal 86. The circuit 84 generally has a power FET 87(Field Effect Transistor) and a power FET 88 with each having a gate, adrain and a source. In the illustrated form, the power FETs 87 and 88each are N-channel devices. A gate-side RF impedance matching network 92is connected between the RF input terminal 85 and the gate of the powerFET 87. A gate-side RF impedance matching network 94 is connectedbetween the RF input terminal 85 and the gate of the power FET 88. Agate-side decoupling circuit 90 is connected between a ground V_(SS)terminal and each of the gates of power FET 87 and power FET 88. Thedrain of each of power FET 87 and power FET 88 is connected to the RFoutput terminal 86. A power supply voltage labeled V_(DD) is connectedto the drains of power FET 87 and power FET 88 at the RF output terminal86. Each of power FET 87 and power FET 88 has a source connected to theground V_(SS) terminal. A conductor having an inductive element in theform of an inductance 95 that is inherent in the conductive material ofthe conductor is connected between the RF input terminal 85 and a node96. It should be understood that the conductor may be implemented invarious forms. For example, a conductive or metal wire may be used asthe conductor. A conductive layer or conductive strip commonly used insemiconductor manufacturing may be implemented from any of variousconductive materials, such as metals including copper, tungsten andvarious metal alloys. A first electrode of an RF matching capacitor 98is connected to node 96. A second electrode of the capacitor 98 isconnected to the ground V_(SS) terminal. The node 96 is connected to thegate of the power FET 87 by a conductor having an inductance 97 that isinherent in the conductive material of the conductor.

Within the gate-side decoupling circuit 90, a node 93 is connected tothe gate of the power FET 87 by a conductor having an inductance 89 thatis inherent in the conductive material of the conductor. Node 93 is alsoconnected to the gate of the power FET 88 by a conductor having aninductance 99 that is inherent in the conductive material of theconductor. A first terminal of a resistor 91 is connected to the node93, and a second terminal of the resistor 91 is connected to a firstelectrode of a low frequency decoupling capacitor 103 via a conductorhaving an inductance 101 that is inherent in the conductive material ofthe conductor. A second electrode of the decoupling capacitor 103 isconnected to the ground V_(SS).

Within the gate-side RF matching network 94, the RF input terminal 85 isconnected to a node 104 via a conductor having an inductance 100 that isinherent in the conductive material of the conductor. A first electrodeof an RF matching capacitor 106 is connected to node 104, and a secondelectrode of the RF matching capacitor 106 is connected to the groundV_(SS). The node 104 is connected via a conductor having an inductance102 that is inherent in the conductive material of the conductor to thegate of the power FET 88 and to the conductor having inductance 99.

On the drain side of power FET 87, an RF matching network is provided byinductances 110 and 112 and an RF matching capacitor 116. A conductorhaving an inductance 110 that is inherent in the conductive material ofthe conductor has a first end connected to the drain of power FET 87 anda second end connected to a node 114. A conductor having an inductance112 that is inherent in the conductive material of the conductor has afirst end connected to the node 114 and a second end connected to the RFoutput terminal 86. A first electrode of the RF matching capacitor 116is connected to node 114. A second electrode of the RF matchingcapacitor 116 is connected to the ground V_(SS).

On the drain side of power FET 88, an RF matching network is provided byinductances 118 and 120 and an RF matching capacitor 124. A conductorhaving an inductance 118 that is inherent in the conductive material ofthe conductor has a first end connected to the drain of power FET 88 anda second end connected to a node 122. A conductor having an inductance120 that is inherent in the conductive material of the conductor has afirst end connected to the node 122 and a second end connected to the RFoutput terminal 86. A first electrode of the RF matching capacitor 124is connected to node 122. A second electrode of the RF matchingcapacitor 124 is connected to the ground V_(SS).

In operation, circuit 84 uses a decoupling circuit only on the gate sideof the power FETs. An RF signal is received at the RF input terminal 85and is amplified and provided at an RF output terminal 86 which issuperimposed onto the terminal for the supply voltage V_(DD). Adecoupling circuit, in the form of decoupling circuit 90, is provided incircuit 84 only on the gate side of power FETs 87 and 88. Capacitors 98and 106 respectively function as RF matching capacitors for impedancematching purposes as previously described. The decoupling circuit 90functions analogous to the gate side decoupling circuit 34 of circuit 20and thus a detailed functional description will not be repeated.Impedance matching networks 92 and 94 function to provide an impedanceon the gate side of power FETs 87 and 88, respectively. On the drainside of power FETs 87 and 88, the capacitive value of respectivecapacitors 116 and 124 is low and shifts the low frequency resonance upin frequency. Thus there is no need for the decoupling circuit that ison the gate side to be used on the drain side.

Illustrated in FIG. 5 is a circuit 130 that is a portion of anotherpower amplifier in accordance with another form. An RF input terminal132 is connected to a first terminal of an inductance 140 that isinherent in a conductor connected to the RF input terminal 132. A secondterminal of inductance 140 is connected to a first electrode or firstterminal of an RF impedance matching capacitor 146 at a node 144. Asecond terminal of capacitor 146 is connected to a V_(SS) power supplyterminal. The second terminal of inductance 140 is also connected to afirst terminal of an inductance 142 which is also an inherentinductance. A second terminal of inductance 142 is connected to acontrol electrode or gate of an RF power transistor 136. The gate oftransistor 136 is connected to a gate side decoupling circuit 138. Thedecoupling circuit 138 has a first terminal of an inductance 148connected to the gate of transistor 136. A second terminal of inductance148 is connected to a first terminal of a resistor 150. A secondterminal of resistor 150 is connected to a first terminal of aninductance 152. A second terminal of inductance 152 is connected to afirst terminal of a capacitor 156 at a node 154. A second terminal ofcapacitor 156 is connected to the V_(SS) power supply terminal. The RFpower transistor 136 is an N-channel transistor in the illustrated form.A source of transistor 136 is connected to the V_(SS) power supplyterminal. A drain of transistor 136 is connected to a first terminal ofboth an inductance 160 and inductance 162. Inductance 160 and inductance162 each represent an inherent inductance associated with theillustrated conductor. A second terminal of inductance 162 is connectedto an RF output terminal 134 and to a positive power supply terminallabeled V_(DD). A second terminal of inductance 160 is connected to adrain side decoupling circuit 168 and to a first terminal of a capacitor164 at a node 166. A second terminal of capacitor 164 is connected tothe V_(SS) power supply terminal. The drain side decoupling circuit 168has a first terminal of an inductance 170 connected to the node 166. Asecond terminal of inductance 170 is connected to a first terminal of aresistor 172. A second terminal of resistor 172 is connected to a firstterminal of an inductance 174. A second terminal of the inductance 174is connected to a first terminal of a capacitor 178 at a node 176. Asecond terminal of capacitor 178 is connected to the V_(SS) power supplyterminal. Inductance 170 and inductance 174 of the drain side decouplingcircuit 168 each represent an inherent inductance associated with theillustrated conductor.

In operation, circuit 130 implements a single power FET amplificationcircuit. On the gate side, both an RF impedance matching network and adecoupling circuit are used. Similarly, on the drain side, both an RFimpedance matching network using capacitor 164 and the decouplingcircuit 168 are provided. Their operational function on the drain sideof power FET 136 is the same as was described for the drain sidematching network and decoupling circuit of FIG. 3 and thus will not berepeated. When the output RF signal is at node 166, the impedancepresented by the decoupling circuit 168 is high and thus virtually allof the RF signal is sent through capacitor 164. The impedance ofcapacitor 164 at RF frequencies is low enough that the RF signal is notsignificantly attenuated by capacitor 164. Thus the gain of the RFsignal at terminal 134 is not significantly degraded by either the RFimpedance matching network or the decoupling circuit 168. Similarly, onthe gate side of power FET 136 the functionality of capacitor 146 andthe decoupling circuit 138 is similar to that described in connectionwith the RF impedance matching network and decoupling circuit for FIGS.3 and 4 and will not be repeated. It should be noted that in anotherform circuit 130 may be modified to operate without the use of thedecoupling circuit 168 on the drain side. In this form there is gateside baseband termination provided by the decoupling circuit 138 andonly an RF impedance matching function on the drain side. In anotherform, the decoupling circuit 168 may be used on the drain side with onlyan RF impedance matching function used on the gate side.

Illustrated in FIG. 6 is a circuit 200 that is a portion of anotherpower amplifier in accordance with another form. An RF input terminal202 is connected to a first terminal of an inductance 210. A secondterminal of the inductance 210 is connected at a node 214 to a firstterminal of an RF impedance matching capacitor 216. A second terminal ofthe RF impedance matching capacitor 216 is connected to a V_(SS) supplyvoltage terminal. A first terminal of an inductance 212 is connected tothe first terminal of the capacitor 216. A second terminal of inductance212 is connected to a gate of an RF power transistor 206 or power FETand to a first terminal of an inductance 218. A second terminal of theinductance 218 is connected to a first terminal of an inductance 226 ata node 220 and to a first terminal of a capacitor 222 at the node 220. Afirst terminal of the resistor 228 is connected to a second terminal ofthe inductance 226. A second terminal of the resistor 228 is connectedto a first terminal of a capacitor 224. A second terminal of capacitor224 is connected to the V_(SS) supply voltage terminal. A secondterminal of the capacitor 222 is also connected to the first terminal ofthe capacitor 224. In the illustrated form the RF power transistor 206is an N-channel transistor. A source of RF power transistor 206 isconnected to the V_(SS) supply voltage terminal. A drain of RF powertransistor 206 is connected to a first terminal of inductance 232. Asecond terminal of inductance 232 is connected to an RF output terminal204 and to a V_(DD) supply voltage terminal. The drain of RF powertransistor 206 is also connected to a first terminal of an inductance230. A second terminal of inductance 230 is connected to a firstterminal of a capacitor 164 at a node 234. A second terminal ofcapacitor 164 is connected to the V_(SS) supply voltage terminal. Afirst terminal of an inductance 235 is connected to the first terminalof capacitor 164 at node 234. A second terminal of inductance 235 isconnected to a first terminal of an inductance 244 at a node 238 and toa first terminal of a capacitor 240. A second terminal of the inductance244 is connected to a first terminal of a resistor 246. A secondterminal of resistor 246 is connected to a first terminal of a capacitor242. A second terminal of capacitor 242 is connected to the V_(SS)supply voltage terminal. A second terminal of capacitor 240 is connectedto the first terminal of the capacitor 242 and to the second terminal ofthe resistor 246. Each of inductance 210, inductance 212, inductance218, inductance 226, inductance 230, inductance 232, inductance 235 andinductance 244 is an inductive element that is inherent in a conductorof circuit 200.

In operation, circuit 200 uses both an RF impedance matching network anda decoupling network on the gate side of a power FET and on the drainside of the power FET. In this form the decoupling networks on the gateside (inductance 226, resistor 228, capacitor 222 and capacitor 224) anddrain side (inductance 244, resistor 246, capacitor 240 and capacitor242) is formed with a capacitor in parallel with an inductance in serieswith a resistor. This form of RF decoupler also functions to present ahigh impedance in the passband range of frequencies, both on the gateside of RF power transistor 206 and on the drain side of RF powertransistor 206. The decoupling networks are functional in the low bandrange of frequencies. The decoupling networks provide a low frequencytermination to ground for the distortion products that develop due toenvelope frequencies. The decoupling networks, in the absence ofresistor 228 or resistor 246, exhibit a low frequency resonance which isundesired. In particular, the inductance and capacitance create anunwanted resonance in the 1 to 20 MHz range which interferes withpre-distortion linearization and creates a high impedance at very lowbaseband frequencies. However, resistors 228 and 246 are respectivelyinserted between the gate or drain of the RF power transistor 206 andcapacitors 224 and 242, respectively, to dampen or attenuate the lowfrequency resonance created by the respective decoupling networks. Thelow frequency resonance which is dampened by each resistor is at afrequency that is lower than an RF frequency.

In alternatives to the form illustrated in FIG. 6 it should beappreciated that the nodes 220 and 234 of the respective gate side anddrain side decoupling circuits may be connected to the power FET atdiffering points. In an alternative form on the gate side for example,the decoupling circuit may be physically connected at the physicallocation of the RF input terminal.

Illustrated in FIG. 7 is the gate side portion of a circuit 250 that isa portion of another power amplifier in accordance with another form. AnRF input terminal 252 is connected to a first terminal of an inductance254. A second terminal of inductance 254 is connected to a firstterminal of an RF impedance matching capacitor 256 and to a firstterminal of an inductance 258. A second terminal of capacitor 256 isconnected to the V_(SS) supply voltage terminal. A second terminal ofinductance 258 is connected to a gate or control electrode of an RFpower transistor 260 (i.e. RF power FET). The gate of the RF powertransistor 260 is also connected to a first terminal of an inductance266. A second terminal of the inductance 266 is connected to a firstterminal of a resistor 262. A second terminal of resistor 262 isconnected to a first terminal of a capacitor 264. A second terminal ofthe capacitor 264 is connected to the V_(SS) supply voltage terminal.

In operation, the capacitor 256 functions as an RF impedance matchingcapacitor and the inductance 266, resistor 262 and capacitor 264function as a decoupling circuit for the gate side of the RF powertransistor 260. It should be appreciated that a similar RF impedancematching network and decoupling circuit may be provided on the drainside of the RF power transistor 260. The decoupling circuit uses aresistance for the purpose of dampening a resonance at a frequency lowerthan an RF frequency. However, instead of the resistance being aseparate resistor, resistance is incorporated into the capacitor 264 asa composite structure. In this form a thin film resistor or other lossycomponent is integrated into the capacitor structure. The presence of aresistive thin film sufficiently dampens the previously discussedresonance which the decoupling circuit creates at low frequency.

Illustrated in FIG. 8 is a circuit 300 that is a portion of anotherpower amplifier in accordance with another form. A first RF inputsignal, RF Input 1, is coupled to a terminal 302 that is connected to anode 311 via an inductance 310 which represents an inherent inductiveelement of a conductor. A first electrode of a capacitor 316 isconnected to node 311 and a second electrode of the capacitor 316 isconnected to a supply voltage labeled V_(SS). In one form V_(SS) may beimplemented as ground. A first terminal of an inductance 312 isconnected to node 311 and a second terminal of inductance 312 isconnected to a gate of an RF power transistor 314 which is an N-channeltransistor. A source of transistor 314 is connected to V_(SS). A drainof transistor 314 is connected to a first terminal of an inductance 330.A first terminal of an inductance 332 is also connected to the drain oftransistor 314. A second terminal of inductance 332 is connected to afirst RF output labeled RF Output 1. A supply voltage V_(DD) isconnected to the RF Output 1. A second terminal of inductance 330 isconnected to a node 336. A first electrode of a capacitor 334 isconnected to node 336, and a second electrode of capacitor 334 isconnected to V_(SS). A first terminal of an inductance 338 is connectedto node 336, and a second terminal of inductance 338 is connected to afirst terminal of a resistor 340. A second terminal of resistor 340 isconnected to a first terminal of an inductance 342. A second terminal ofthe inductance 342 is connected to a first electrode of a capacitor 344.A second electrode of capacitor 344 is connected to V_(SS).

A second RF input signal, RF Input 2, is coupled to a terminal 304 thatis connected to a node 319 via an inductance 318 which represents aninherent inductive element of a conductor. A first electrode of acapacitor 324 is connected to node 319 and a second electrode of thecapacitor 324 is connected to a supply voltage labeled V_(SS). A firstterminal of an inductance 320 is connected to node 319 and a secondterminal of inductance 320 is connected to a gate of an RF powertransistor 322 which is an N-channel transistor. A source of transistor322 is connected to V_(SS). A drain of transistor 322 is connected to afirst terminal of an inductance 348. A first terminal of an inductance346 is also connected to the drain of transistor 322. A second terminalof inductance 346 is connected to a second RF output labeled RF Output2. The supply voltage V_(DD) is connected to the RF Output 2. A secondterminal of inductance 348 is connected to a node 351. A first electrodeof a capacitor 350 is connected to node 351, and a second electrode ofcapacitor 350 is connected to V_(SS). A first terminal of an inductance352 is connected to node 351, and a second terminal of inductance 352 isconnected to the first terminal of resistor 340. All illustratedinductances within circuit 300 are inherent inductive elements of aconductor.

In operation, circuit 300 is a dual RF path circuit that is inpush-pull, balanced, or a Doherty configuration. There is no decouplingcircuit on the gate side of either RF power transistor 314 or RF powertransistor 322. Each of the RF power transistors is biased separately bythe gate voltage V_(G1) and V_(G2). On the drain side, the same D.C.voltage, VDD, is present on each drain. Therefore, a common decouplingcircuit may be used for both RF output signal paths.

Illustrated in FIG. 9 is a circuit 360 that is a portion of anotherpower amplifier in accordance with another form. A first RF inputsignal, RF Input 1, is coupled to a terminal 362 that is connected to anode 375 via an inductance 370 which represents an inherent inductiveelement of a conductor. A first electrode of a capacitor 374 isconnected to node 375 and a second electrode of the capacitor 374 isconnected to a supply voltage labeled V_(SS). In one form V_(SS) may beimplemented as ground. A first terminal of an inductance 372 isconnected to node 375 and a second terminal of inductance 372 isconnected to a gate of an RF power transistor 376 which is an N-channeltransistor. A source of transistor 376 is connected to V_(SS). A drainof transistor 376 is connected to a first terminal of an inductance 386.A first terminal of an inductance 388 is also connected to the drain oftransistor 314. A second terminal of inductance 388 is connected to afirst RF output labeled RF Output 1 at a terminal 366. A supply voltageV_(DD) is connected to the RF Output 1. A second terminal of inductance386 is connected to a node 391. A first electrode of a capacitor 390 isconnected to node 391, and a second electrode of capacitor 390 isconnected to V_(SS). A first terminal of a resistor 392 is connected tonode 391, and a second terminal of resistor 392 is connected to a firstterminal of an inductance 394. A second terminal of inductance 394 isconnected to a first electrode of a capacitance 396. A second electrodeof the capacitance 396 is connected to V_(SS).

A second RF input signal, RF Input 2, is coupled to a terminal 364 thatis connected to a node 381 via an inductance 378. A first electrode of acapacitor 382 is connected to node 381 and a second electrode of thecapacitor 382 is connected to the V_(SS) supply voltage. A firstterminal of an inductance 380 is connected to node 381 and a secondterminal of inductance 380 is connected at a node 379 to a gate of an RFpower transistor 384 which is an N-channel transistor. A gate-sidedecoupling circuit is formed by inductance 383, resistor 385 and acapacitor 387. A first terminal of inductance 383 is connected to thenode 379. A second terminal of inductance 383 is connected to a firstterminal of a resistor 385. A second terminal of resistor 385 isconnected to a first electrode of a capacitor 387. A second electrode ofthe capacitor 387 is connected to V_(SS). A source of transistor 384 isconnected to V_(SS). A drain of transistor 384 is connected to a firstterminal of an inductance 398. A second terminal of inductance 398 isconnected to a first terminal of an inductance 402 and to a firstelectrode of a capacitor 400 at a node 401. A second terminal ofinductance 402 is connected to a second RF output labeled RF Output 2 ata terminal 368. The supply voltage V_(DD) is connected to the RF Output2. A second terminal of capacitor 400 is connected to the V_(SS) supplyvoltage. All illustrated inductances within circuit 360 are inherentinductive elements of a conductor.

In operation, circuit 360 is again a dual RF path circuit that is inpush-pull, balanced, or a Doherty configuration. There is a decouplingcircuit on the gate side of only one RF power transistor 376 and adecoupling circuit on the drain side of only the other RF powertransistor 384. Each of the RF power transistors is biased separately bythe gate voltage V_(G1) and V_(G2). On the drain side, either the sameor differing D.C. voltages, V_(DD1) and V_(DD2), are present on eachdrain. The RF power transistor 376 has a shunt-L output and uses a drainbaseband termination. The RF power transistor 384 has a T-match outputand uses a gate baseband termination. The gate and drain basebandterminations can be used independently of each other. Different externaloutput networks would be used for the RF output 1 and the RF output 2.

Illustrated in FIG. 10 is a decoupling network 34′ which may be used inlieu of any of the illustrated decoupling networks, including decouplingnetwork 34 of FIG. 3. When used as a replacement for decoupling network34, the decoupling network 34′ has an inductance 406 having a firstterminal that would connect with the gate of power FET 26 of FIG. 3. Asecond terminal of inductance 406 is connected to a first terminal of aresistor 408. A second terminal of resistor 408 is connected to a firstterminal of a resistor 414 and to a first terminal of a resistor 410 ata node 409. A second terminal of resistor 414 is connected to a firstterminal of an inductance 416. A second terminal of inductance 416 isconnected to a first electrode of a capacitor 418. A second electrode ofcapacitor 418 is connected to a terminal for receiving V_(SS). A secondterminal of resistor 410 is connected to a first terminal of aninductance 412. A second terminal of inductance 412 would connect withthe gate of power FET 28 of FIG. 3. All illustrated inductances withincircuit 34′ are inherent inductive elements of a conductor.

In operation, decoupling network 34′ utilizes resistor 408 in one signalpath branch and utilizes resistor 410 is the other signal path branch inaddition to using a common resistor 414 in a common branch to the twosignal paths. In this way the resistance is distributed and functions todampen the low frequency resonance which is introduced by using adecoupling network with pre-distortion. Resistor 414 is optional, as theresistance it provides can be distributed in resistors 408 and 410.

Illustrated in FIG. 11 is a circuit 450 that is a portion of anotherpower amplifier in accordance with another form. An RF input signal iscoupled to an RF input terminal 452 and an amplified RF output signal isprovided at an RF output terminal 454. A gate bias, V_(G), is connectedto the input terminal 452. The circuit 450 generally has a power FET 456(Field Effect Transistor) and a power FET 458 with each having a gate, adrain and a source. In the illustrated form, the power FETs 456 and 458each are N-channel devices. A gate-side RF impedance matching networkhaving a capacitor 464 and inductances 460 and 462 is connected betweenthe RF input terminal 452 and the gate of the power FET 456. Inductance460 has a first terminal connected to the RF input 452 and a secondterminal connected to a first electrode of capacitor 464 and a firstterminal of inductance 462 at a node 461. A second electrode ofcapacitor 464 is connected to V_(SS). A second terminal of inductance462 is connected to the gate of the power FET 456 at a node 465. Agate-side RF impedance matching network in the form of a capacitor 478and inductances 476 and 480 is connected between the RF input terminal452 and the gate of the power FET 458. Inductance 476 has a firstterminal connected to the RF input terminal 452 and a second terminalconnected to a first electrode of a capacitor 478 and a first terminalof an inductance 480 at a node 477. A second electrode of capacitor 478is connected to V_(SS). A second terminal of inductance 480 is connectedto the gate of power FET 458 at a node 475. A gate-side decouplingcircuit in the form of inductances 466, 472 and 468, capacitor 474 andresistor 470 is connected between the V_(SS) terminal and each of thegates of power FET 456 and power FET 458. In particular, a firstterminal of inductance 466 is connected to the gate of power FET 456 atnode 465. A second terminal of inductance 466 is connected to a firstterminal of resistor 470 and to a first terminal of inductance 468 at anode 467. A second terminal of inductance 468 is connected to the gateof the power FET 458 at a node 475. A second terminal of resistor 470 isconnected to a first terminal of inductance 472. A second terminal ofinductance 472 is connected to a first electrode of a capacitor 474. Asecond electrode of capacitor 474 is connected to the V_(SS) terminal.

A drain-side RF impedance matching network in the form of inductances480 and 482 and capacitor 484 is provided for the power FET 456. Adrain-side impedance matching network in the form of inductances 496,498 and capacitor 500 is provided. A first terminal of each ofinductance 480 and inductance 482 is connected to the drain of the powerFET 456. A second terminal of inductance 482 is connected to the RFoutput at terminal 454. A second terminal of inductance 480 is connectedto a first electrode of capacitor 484 at a node 486. A second electrodeof capacitor 484 is connected to the V_(SS) terminal. A first terminalof each of inductance 496 and inductance 498 is connected to the drainof the power FET 458. A second terminal of inductance 496 is connectedto the RF output at terminal 454. A second terminal of inductance 498 isconnected to a first electrode of capacitor 500 at a node 501. A secondelectrode of capacitor 500 is connected to the V_(SS) terminal. Adrain-side decoupling network in the form of inductances 488, 502 and492, resistor 490 and capacitor 494 is provided. A first terminal of aninductance 488 is connected to node 486, and a second terminal ofinductance 488 is connected to a first terminal of a resistor 490 at anode 489. A second terminal of resistor 490 is connected to a firstterminal of an inductance 492. A second terminal of inductance 492 isconnected to a first electrode of capacitor 494. A second electrode ofcapacitor 494 is connected to the V_(SS) terminal. The V_(DD) powersupply is connected to node 486 via inductance 504 rather than beingconnected to the RF output at terminal 454. The V_(DD) power supply isalso connected to node 501 via inductance 506. A first terminal of aninductance 506 is connected is connected to V_(DD). A second terminal ofinductance 506 is connected to node 501. All illustrated inductanceswithin circuit 450 are inherent inductive elements of a conductor.

In operation, circuit 450 uses two separate D.C. voltage pins orterminals wherein V_(DD) is connected via an inductive componentconductor to node 486 and node 501. When V_(DD) is applied to thesenodes as opposed to the RF output terminals, the parallel inductanceformed by inductance 504 being in parallel with inductances 480 and 482moves the resonance higher in frequency. As a result, no λ/4 signaltermination is needed. Thus a user of circuit 450 will have a smallersized product. It should be understood that the separate D.C. pins maybe used on the drain side with either a single RF output terminal orwith two RF output terminals.

The use of separate D.C. pins or terminals may also be applied to thegate side of RF power transistors 456 and 458. In particular, ratherthan applying the V_(G) gate bias to input terminal 452, the D.C.voltage may be applied to node 465 and to node 475. Either separatevalues of V_(G), such as V_(G1) and V_(G2), may be used or a same gatevoltage may be applied to both of nodes 465 and 475. Whether separatepins are used only on the gate side, the drain side or on both sides,the effect of all of these variations is to move the resonance caused bya decoupling circuit using pre-distortion to a higher frequency.

Illustrated in FIG. 12 is a graphical representation of a two-tonefrequency response of a power amplifier that uses a conventionaldecoupling circuit. The vertical axis is the signal strength of thirdorder intermodulation distortion. The horizontal axis is frequencyspacing of the two tones. The values which are provided are forexplanation purposes only and are exemplary. The values are dependentupon various factors, including semiconductor processing parameters.There is an upper third order intermodulation distortion signal 602 anda lower third order intermodulation distortion signal 600. Bothintermodulation distortion signals exhibit a pronounced resonance in thelower band between ten and one hundred MHz.

Illustrated in FIG. 13 is a graphical representation of a conventionalpower amplifier that uses a prior art decoupling circuit. The verticalaxis is again the signal strength of third order intermodulationdistortion. The horizontal axis is frequency spacing of the two tones.The values which are provided are for explanation purposes only and areexemplary. The values are dependent upon various factors, includingsemiconductor processing parameters. There is an upper third orderintermodulation distortion signal 606 and a lower third orderintermodulation distortion signal 604. While the resonance between tenand one hundred MHz has been shifted up in frequency, additionaldistortion has been added below ten MHz. In one exemplary form, thisresonance is present at around six MHz, but the location of theresonance is dependent upon process specifications and parameters.

Illustrated in FIG. 14 is a graphical representation of a poweramplifier that uses a decoupling circuit embodying principles of thepresent invention. The vertical axis is again the signal strength ofthird order intermodulation distortion. The horizontal axis is frequencyspacing of the two tones. The values which are provided are forexplanation purposes only and are exemplary. The values are dependentupon various factors, including semiconductor processing parameters.There is an upper third order intermodulation distortion signal 610 anda lower third order intermodulation distortion signal 608. With thedampening provided by one or more resistors in a decoupling circuit, asubstantially linear frequency response in the low band is obtained. Thepreviously introduced resonance between ten and one hundred MHz has beenshifted higher in frequency, in addition to the unwanted distortionbelow ten MHz being removed.

It should be understood that other alternatives of the gate and/or drainside decoupling network for a power FET include can incorporate theresistor which performs the dampening function into the power FET itselfwith resistance added to the gate structure of the power FET. Varioussemiconductor gate structures may be created to implement a resistivecomponent for a gate of a power FET. Also, while various embodimentsdescribed herein have detailed a dual RF signal path configuration, itshould be understood that any integer number of RF paths may beimplemented.

By now it should be appreciated that there has been provided a radiofrequency (RF) power transistor circuit having a first power transistorhaving a control electrode coupled to an input terminal for receiving anRF input signal. The first power transistor has a first currentelectrode for providing an RF output signal at an output terminal, and asecond current electrode coupled to a power supply voltage terminal. Afirst decoupling circuit has a first inductive element, a firstresistor, and a first capacitor coupled together in series between thecontrol electrode of the first power transistor and the power supplyvoltage terminal. The first decoupling circuit is for dampening aresonance at a frequency lower than an RF frequency. In one form the RFpower transistor circuit further has a second power transistor having acontrol electrode coupled to both the RF input terminal and to the firstdecoupling circuit, a first current electrode coupled to the RF outputterminal, and a second current electrode coupled to the power supplyvoltage terminal. In another form the RF power transistor circuitfurther has a second decoupling circuit. The second decoupling circuithas a second inductive element, a second resistor, and a secondcapacitor coupled together in series between the first current electrodeof the first power transistor and the power supply voltage terminal. Inanother form a resistance value of the first resistor is in a range of0.5 ohms to 5 ohms. In another form a capacitance value of the firstcapacitor is in a range of 10 nano Farads to 1,000 nano Farads. In yetanother form an inductance value of the first inductive element is in arange of 0.1 nano Henry to 3 nano Henrys. In yet another form the firstinductive element has a first terminal coupled to the control electrodeof the first power transistor, and a second terminal. The first resistorhas a first terminal coupled to the second terminal of the firstinductive element, and a second terminal. The first capacitor has afirst electrode coupled to the second terminal of the resistor, and asecond electrode coupled to the power supply voltage terminal. The RFpower transistor circuit further has a second capacitor having a firstelectrode coupled to the first terminal of the first inductive element,and a second electrode coupled to the first electrode of the firstcapacitor. In another form the RF power transistor circuit further has asecond decoupling circuit having a second inductive element having afirst terminal coupled to the first current electrode of the first powertransistor, and a second terminal. A second resistor has a firstterminal coupled to the second terminal of the second inductive element,and a second terminal. A third capacitor has a first electrode coupledto the second terminal of the second resistor, and a second electrode. Afourth capacitor has a first electrode coupled to the first terminal ofthe second inductive element, and a second electrode coupled to thefirst electrode of the third capacitor. In another form the RF powertransistor circuit further has an RF impedance matching network having asecond inductive element having a first terminal coupled to the controlelectrode of the first power transistor, and a second terminal. A secondcapacitor has a first electrode coupled to the second terminal of thesecond inductive element, and a second electrode coupled to the powersupply voltage terminal. The RF impedance matching network is forpreventing a current at the first electrode of the second capacitor whenthe RF power transistor circuit is operating at an RF frequency.

In another form a radio frequency (RF) power transistor circuit isprovided having a first power transistor having a control electrodecoupled to an input terminal for receiving a radio frequency inputsignal. A first current electrode provides an RF output signal at anoutput terminal, and a second current electrode is coupled to a powersupply voltage terminal. A first decoupling circuit has a firstinductive element, a first resistor, and a first capacitor coupledtogether in series between the first current electrode of the firstpower transistor and the power supply voltage terminal. The firstdecoupling circuit is for dampening a resonance at a frequency lowerthan an RF frequency. In one form a resistance value of the firstresistor is in a range of 0.5 ohms to 5 ohms. In another form acapacitance value of the first capacitor is in a range of 10 nano Faradsto 1,000 nano Farads. In yet another form an inductance value of thefirst inductive element is in a range of 0.1 nano Henry to 3 nanoHenrys. In yet another form the RF power transistor circuit further hasa second power transistor having a control electrode coupled to the RFinput terminal, a first current electrode coupled to both the RF outputterminal and to the first decoupling circuit, and a second currentelectrode coupled to the power supply voltage terminal. In another formthe RF power transistor circuit further has a second decoupling circuit,the second decoupling circuit having a second inductive element, asecond resistor, and a second capacitor coupled together in seriesbetween the control electrode of the first power transistor and thepower supply voltage terminal. In yet another form the RF powertransistor circuit of claim 15, further comprising a second powertransistor having a control electrode coupled to both the RF inputterminal and to the first decoupling circuit, a first current electrodecoupled to both the RF output terminal and to the second decouplingcircuit, and a second current electrode coupled to the power supplyvoltage terminal.

In another form there is herein provided a radio frequency (RF) powertransistor circuit having a first power transistor having a controlelectrode coupled to an input terminal for receiving an RF input signal.A first current electrode of the first power transistor provides an RFoutput signal at an output terminal, and a second current electrode ofthe first power transistor is coupled to a power supply voltageterminal. A second power transistor has a control electrode coupled tothe control electrode of the first power transistor, a first currentelectrode coupled to the first current electrode of the first powertransistor, and a second current electrode coupled to the power supplyvoltage terminal. A first decoupling circuit has a first inductiveelement, a first resistor, and a first capacitor coupled together inseries between the coupled together control electrodes of the first andsecond power transistors and the power supply voltage terminal. A seconddecoupling circuit has a second inductive element, a second resistor,and a second capacitor coupled together in series between the coupledtogether first current electrodes of the first and second powertransistors and the power supply voltage terminal. In another form aresistance value of each of the first and second resistors is in a rangeof 0.5 ohms to 5 ohms. In one form a capacitance value of each of thefirst and second capacitors is in a range of 10 nano Farads to 1,000nano Farads and an inductance value of each of the first and secondinductive elements is in a range of 0.1 nano Henry to 3 nano Henrys. Inyet another form the first and second decoupling circuits are fordampening a resonance at a frequency lower than an RF frequency. In yetanother form the RF power transistor circuit has a third capacitorhaving a first electrode coupled to the control electrode of the firstpower transistor, and a second electrode coupled to the power supplyvoltage terminal. A fourth capacitor has a first electrode coupled tothe control electrode of the second power transistor, and a secondelectrode coupled to the power supply voltage terminal, wherein thethird and fourth capacitors provide an open circuit at an RF frequency.

Although the invention has been described with respect to specificconductivity types or polarity of potentials, skilled artisansappreciate that conductivity types and polarities of potentials may bereversed. As an alternative, the VSS terminal may be implemented as apotential other than ground wherein the V_(SS) potential is lower inpolarity than the V_(DD) potential.

The term “coupled,” as used herein, is not intended to be limited to adirect coupling or a mechanical coupling. Although the invention isdescribed herein with reference to specific embodiments, variousmodifications and changes can be made without departing from the scopeof the present invention as set forth in the claims below. For example,various types of transistors which are used to implement the illustratedcircuit functions may be implemented, such as MOS (metal oxidesemiconductor), bipolar, GaAs, GaN, silicon on insulator (SOI) andothers. The amount of power supply voltage reduction can be adjustedaccording to specific application requirements. Accordingly, thespecification and figures are to be regarded in an illustrative ratherthan a restrictive sense, and all such modifications are intended to beincluded within the scope of the present invention. Any benefits,advantages, or solutions to problems that are described herein withregard to specific embodiments are not intended to be construed as acritical, required, or essential feature or element of any or all theclaims.

The terms “a” or “an,” as used herein, are defined as one or more thanone. Also, the use of introductory phrases such as “at least one” and“one or more” in the claims should not be construed to imply that theintroduction of another claim element by the indefinite articles “a” or“an” limits any particular claim containing such introduced claimelement to inventions containing only one such element, even when thesame claim includes the introductory phrases “one or more” or “at leastone” and indefinite articles such as “a” or “an.” The same holds truefor the use of definite articles.

Unless stated otherwise, terms such as “first” and “second” are used toarbitrarily distinguish between the elements such terms describe. Thus,these terms are not necessarily intended to indicate temporal or otherprioritization of such elements.

The invention claimed is:
 1. A radio frequency (RF) power transistorcircuit comprising: a power transistor having a control electrode forreceiving an RF input signal, and a current electrode for providing anRF output signal; and a decoupling circuit comprising a first inductiveelement, a resistor, and a first capacitor coupled together in seriesbetween the current electrode of the power transistor and a groundterminal, wherein the first inductive element and the first capacitorform an inductor/capacitor circuit that has a resonance at a frequencybelow a passband range of frequencies for the RF power transistorcircuit, and the resistor is configured to dampen the resonance of theinductor/capacitor circuit; a node coupled to the current electrode,wherein the decoupling circuit is coupled between the node and theground terminal; and a D.C. blocking capacitor coupled in parallel withthe decoupling circuit between the node and the ground terminal.
 2. TheRF power transistor circuit of claim 1, further comprising: a D.C.voltage pin coupled to the current electrode for providing a powersupply voltage to the power transistor circuit.
 3. The RF powertransistor circuit of claim 2, further comprising: an output terminalcoupled to the current electrode, wherein the D.C. voltage pin iscoupled to the output terminal.
 4. The RF power transistor circuit ofclaim 2, further comprising: a second inductive element coupled betweenthe current electrode of the power transistor and a node, wherein thedecoupling circuit is coupled between the node and the ground terminal,and wherein the D.C. voltage pin is coupled to the node.
 5. The RF powertransistor circuit of claim 4, further comprising: a third inductiveelement coupled between the D.C. voltage pin and the node, wherein aparallel inductance is formed by the second and third inductiveelements.
 6. The RF power transistor circuit of claim 1, furthercomprising: a second inductive element coupled between the currentelectrode of the power transistor and the node.
 7. The RF powertransistor circuit of claim 1, further comprising: a second inductiveelement coupled between the current electrode of the power transistorand a node, wherein the decoupling circuit is coupled between the nodeand the ground terminal.
 8. The RF power transistor circuit of claim 7,further comprising: a D.C. blocking capacitor coupled in parallel withthe decoupling circuit between the node and the ground terminal.
 9. TheRF power transistor circuit of claim 1, further comprising: an outputterminal; and a second inductive element coupled between the currentelectrode of the power transistor and the output terminal.
 10. The RFpower transistor circuit of claim 1, wherein the decoupling circuitpresents a high impedance path to RF signals within a passband range offrequencies between 1.6 gigahertz to 3.7 gigahertz.
 11. The RF powertransistor circuit of claim 1, wherein the decoupling circuit provides alow frequency termination to ground for distortion products that developdue to envelope frequencies.
 12. The RF power transistor circuit ofclaim 11, wherein the resonance is 20 megahertz or less.
 13. A radiofrequency (RF) power transistor circuit comprising: a power transistorhaving a control electrode for receiving an RF input signal, and acurrent electrode for providing an RF output signal; and a decouplingcircuit comprising a first inductive element, a resistor, a firstcapacitor, wherein the first inductive element, the resistor, and thefirst capacitor are coupled together in series between the currentelectrode of the power transistor and a ground terminal, wherein thefirst inductive element and the first capacitor form aninductor/capacitor circuit that has a resonance at a frequency below apassband range of frequencies for the RF power transistor circuit, andthe resistor is configured to dampen the resonance of theinductor/capacitor circuit, and wherein the resistor and the firstinductor are coupled in series between second and third nodes, and asecond capacitor coupled between the second and third nodes in parallelwith the resistor and the first inductor.
 14. A radio frequency (RF)power transistor circuit comprising: a power transistor having a controlelectrode for receiving an RF input signal, and a current electrode forproviding an RF output signal; and a first decoupling circuit comprisinga first inductive element, a first resistor, a first capacitor, whereinthe first inductive element, the first resistor, and the first capacitorare coupled together in series between the control electrode of thepower transistor and a ground terminal, wherein the first inductiveelement and the first capacitor form a first inductor/capacitor circuitthat has a resonance at a frequency below a passband range offrequencies for the RF power transistor circuit, and the first resistoris configured to dampen the resonance of the first inductor/capacitorcircuit, and wherein the resistor and the first inductor are coupled inseries between second and third nodes, and a second capacitor coupledbetween the second and third nodes in parallel with the resistor and thefirst inductor.
 15. The RF power transistor circuit of claim 14, furthercomprising: an input terminal coupled to the control electrode of thepower transistor, wherein the input terminal is configured to receivethe first RF input signal; and a D.C. voltage pin coupled to the controlelectrode for receiving a bias voltage.
 16. A radio frequency (RF) powertransistor circuit comprising: a power transistor having a controlelectrode for receiving an RF input signal, and a current electrode forproviding an RF output signal; a node coupled to the current electrode;a first decoupling circuit comprising a first inductive element, a firstresistor, and a first capacitor coupled together in series between thecontrol electrode of the power transistor and a ground terminal, whereinthe first inductive element and the first capacitor form a firstinductor/capacitor circuit that has a resonance at a frequency below apassband range of frequencies for the RF power transistor circuit, andthe first resistor is configured to dampen the resonance of the firstinductor/capacitor circuit, wherein the second decoupling circuit iscoupled between the node and the ground terminal; a D.C. blockingcapacitor coupled in parallel with the second decoupling circuit betweenthe node and the ground terminal; and a second decoupling circuitcomprising a second inductive element, a second resistor, and a secondcapacitor coupled together in series between the current electrode ofthe power transistor and the ground terminal, wherein the secondinductive element and the second capacitor form a secondinductor/capacitor circuit that has a resonance at a frequency below thepassband range of frequencies for the RF power transistor circuit, andthe second resistor is configured to dampen the resonance of the secondinductor/capacitor circuit.